1. Technical Field
This invention relates to electromagnetic radiation antenna structures capable of receiving and transmitting radio signals that may include dual orthogonally polarized components.
2. Discussion of Related Art
In a complex urban environment of buildings, structures and obstacles, a radio signal will be reflected and scattered and may not follow a straight line path between a transmitter and receiver. Polarization rotation of the radio signal may occur due to reflection and scattering.
To overcome the effects of polarization rotation, polarization diversity reception is known to be used. Polarization diversity requires an antenna to be able to receive components of a signal of any polarization, both horizontally polarized and vertically polarized signals or any polarization between.
A typical cellular mobile radio base station antenna tower will have one transmit antenna and two receive antennas in a "space diversity" configuration for any sector. The receive antennas are spaced apart with the transmit antenna placed between them. One receive antenna will be in a zone of increased signal strength relative to the other receive antenna, should multi-path scattering effects occur. This arrangement typically requires a complex infrastructure, as three antennas are used in each sector, usually nine to a tower. Such known antenna arrangements are relatively large, expensive and visually unappealing.